Chapter 8 Flashcards
Transmission
Common comparison for Transmission Lines?
- Our highway system
- As trucks deliver goods, Transmission Lines deliver power
How are Transmission Lines recognized?
- Large, tall structures either steel or wood
- Large aluminum conductors
About how far apart are Transmission Line Structures?
1,000’
What is the basic function of a Transmission Line?
To take large amounts of bulk power from a source and transmit it over a distance to a given point where it can be used.
What is the main objective of a Transmission Line?
To deliver power with a minimum of loss.
What is DC?
Direct Current has less line losses and only takes two conductors (+,-) Can be economical for large amounts of power over long distances. But to convert from DC to AC installing the equipment to do so is VERY expensive
How are transmission structures chosen?
Based on the voltage of the line, the right of way size, geographical terrain, weather, size of conductor, and construction considerations.
What is one key consideration in the choice of structure?
Whether two circuits are required immediately or in the future
Common properties of Wood Pole Structures?
- 345kV>
- Construction requirements are relatively simple and components are easily assembled
- Maintenance requirements of testing and treating the pole butts
Common properties of Tubular Steel Poles?
- More aesthetically acceptable and have a longer life span than wooden poles, which decay
- Construction is more complicated with steel poles that use a poured cylindrical base
- Some are direct buried
- More expensive
Common properties of the Lattice-Type Steel?
- Structure built with pieces of angle steel bolted together in a lattice arrangement
- 345kV<
- Good strength characteristics and work well for double circuit configurations
- Take more time to assemble due to number of parts
- More extensive footings which take forever to construct (Separate crew for Footing Construction)
Common properties of insulators?
- As voltage increases, size of insulator increases
- Used to be porcelain and glass insulators, now polymer
What are the common types of insulators?
- Porcelain Suspension
- Porcelain Line Post
- Polymer Suspension
- Polymer Line Post
- Glass Suspension
What is a suspension insulator?
Insulator used to support the full line tension in a dead end configuration, or to support the span weight in a true suspension configuration.
Difference in mechanical ratings of insulators?
Dead end configuration would typically have a higher rating than one in a suspension configuration.
What are conductors typically made of?
Strands from aluminum or some form of aluminum alloy
What is used to add strength in a conductor?
Some conductors are reinforced with steel
How are sizes and types chosen for conductors?
- How much power the line needs to carry
- Length of the line
- Span Lengths
- Weather Environment
- Line Losses
- Cost of the Conductor
What style conductor is used to deliver large amounts of power at extra high voltages over long distances?
Bundled Conductors
What does the term bundled mean?
- More than one conductor per phase
- Typically 2-4 conductors per phase
What are bundled conductors used for?
- Increase the capacity of a line
- Reduce radio noise
- Corona Loss
What is Corona Loss?
- Phenomenon occurs at high voltages, which is the result of the ionization of the air around the conductor.
- Effects are audible and are visible at night
What are the max size Conductors can be?
1-3/4” in Diameter and Weigh 2-1/2lbs per foot
What determines the voltage level of a Transmission Line?
- Length of the line
- Amount of power to be delivered
- Voltage of the existing system
- Cost of Losses
What is a Kilovolt?
1000 Volts
What are the Main Grid voltages?
230kV, 2345kV, 500kV, and 765kV
What are the Subtransmission Voltages?
44kV, 69kV, 115kV,, and 138kV
What do higher voltages require?
- Larger right of way
- Larger Structures
- More Insulation
What do Transmission Lines do for Lightning Protection?
- Some form of “Shielding” or “Static Wires”
- Can be recognized by one or two smaller conductors fastened to the top structures above the phase conductors
- These conductors are grounded and provide a path to ground from lightning surges
What do shield wires do for communications?
- Manufactured with a fiber optic cable in the center so the conductor can perform two functions
1. ) The outer portion of the conductor will conduct the lightning surges to ground.
2. ) The inner fiber optic conductor will provide capacity for voice and data communications
How are transmission lines ran in large cities?
It’s an extremely expensive process and very time consuming but the wires are ran underground
In New York its system uses pipe-type, oil-filled cable, with three insulating cables in one pipe filled with oil for cooling purposes.
How is Right-of-Way determined?
-Based on terrain, existing development etc.
What must a company obtain to construct and maintain a line?
Legal Rights
Why are Right-of-Ways difficult to obtain?
Objections of property owners
What determines the size of the right-of-way?
Voltage of the line, type pf structure and conductor spacing
-Also EMF
For a major transmission lines how long may it take to secure rights?
3-5 years
What must a utility provide to the owner of land?
Reasonable Compensation
What must a Right-of-Way be clear of?
trees, vegetation and anything else that could cause an outage
